The present invention relates to a process for the preparation of stoichiometric bismuth germanate of formula Bi.sub.4 Ge.sub.3 O.sub.12. More specifically, it relates to the preparation of a polycrystalline powder of bismuth germanate Bi.sub.4 Ge.sub.3 O.sub.12 having purity and homogeneity characteristics appropriate for the production of bismuth germanate monocrystals usable as scintillators.
Hitherto, bismuth germanate powder has been prepared by using dry methods generally based on oxides of bismuth and germanium, preferably working in a fluidized bed or a rotary oven at temperatures above 600.degree./700.degree. C.
On adopting this procedure, there is only a partial synthesis and the yields obtained are generally approximately 65 to 85%. This poor yield is on the one hand due to the limited acid--base interaction between germanium oxide GeO.sub.2 and bismuth oxide Bi.sub.2 O.sub.3 and on the other hand to the appearance of GeO.sub.2 in quadratic form and which is remarkably inert. Thus, at the end of the operation bismuth germanate Bi.sub.4 Ge.sub.3 O.sub.12 is obtained, which is accompanied by other compounds, such as Bi.sub.12 GeO.sub.20, hexagonal GeO.sub.2 and quadratic GeO.sub.2, which leads to problems for the subsequent production of high purity bismuth germanate monocrystals.